The building block approach to the synthesis of polyoxotrisalkoxometalates

Several novel polyoxonuclear molybdenum and tungsten complexes incorporating trisalkoxo ligands have been prepared and characterized by single S-ray diffraction and H-1- and (1)3C-NMR in solution. The structure of the complexes [W2O4(RC(CH2O)(3))(2)](2-) is similar to that of their previously reported molybdenum analogues. The isostructural complexes [M4O10(MeC(CH2O)(3))(2)](2-) (M = Mo, W) display the rhomb-like compact arrangement based on four edge-sharing octahedra which is common to many tetrametalates, but they differ from previous examples in the coordination mode of the trisalkoxo ligands. The structure of the mixed-valence species [Mo8O18Cl4{MeC(CH2O)(3)}(2)](2-) can be viewed as resulting from the condensation of two thomb-like {Mo-4} units, and is related to that of derivatized-octamolybdates of the type [Mo8O26X2]((2n + 4)-) In contrast, the complex [Mo8O22(OH)(2){MeC(CH2O)(3)}(2)](4-) is composed of two [MO3O9(OH){MeC(CH2O)(3)}](4-) units, formally related to the already known complex [Mo3O7{MeC(CH2O)(3)}(2)](2-), linked by two cis-{MoO2}(2+) units. Finally, the anion [Mo14O7{MeC(CH2O)(3)}(6)](6-) may be viewed as the product of the condensation of one [Mo8O24{MeC(CH2O)(3)}(2)](6-) unit with two [Mo3O7{MeC(CH2O)(3)}(2)](2-) units by sharing corners. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.